This invention relates to a device for shifting a compensator roller in a printing press.
It is a well known fact that printing presses, and rotary printing presses especially, comprise rollers for guiding a paper web through the machine, as well as to correct any out-of-register condition. At least one roller cooperates with each printing unit which functions as a compensator roller and is mounted, to that aim, for up-down movement, whereby it can assume either an uppermost position or lowermost position relative to the stationary structure of the rotary printing press. For controllably shifting this compensator roller between such extreme positions, a conventional gearing is provided which is driven by a controllable motor, such as a DC motor, via vertically extending parallel threaded shafts which are drivingly connected to end hubs on the horizontally positioned compensator roller, to thus enable the compensator roller to be accurately raised and lowered.
It is also known that when feeding a paper web into a rotary press during printing start-ups or whenever the paper web breaks in the course of a printing operation, chains are usually provided on either longitudinal side of the rotary machine structure, which chains are trained around sprocket wheels and interconnected at intervals by crosswise extending rods whereto the start end of the paper web to be led through the machine may be hitched where required.
For construction reasons, two of said sprocket wheels are to be mounted at locations above the uppermost position of the compensator roller in the corresponding printing unit. In view of this compensator roller not being normally located at its uppermost position but rather at some intermediate position or even further toward the lowermost position thereof, considerable difficulty was experienced heretofore in this area of the machine as the paper web was being transported. The paper web being first transported straight upwards by the cross rod connected to the parallel drive chains, and then moved down again along the chain path. If in this critical situation of paper guiding, the compensator roller happens to be at an intermediate position or possibly at its lowermost position, the inevitable result was that the paper web was left unsupported and unguided during the chain downward movement. Since it was unsupported, the paper web was apt to arrange itself in uneven loops above the trailing paper guide roller, which would come ahead of the compensator roller, with the risk of entangling itself around the guiding roller and being torn off.
To avoid this problem, known rotary printing presses required that the paper web be introduced into the machine with the utmost care and attention, while the speed of the feed-in chains must be slowed considerably (down to approximately 6 m/min), which lengthens the paper web introduction time quite significantly, especially because of the large size of a rotary press.